Blossom thinners reduce crop load and increase fruit size and quality of peaches

The purpose of this research was to determine the effectiveness of three blossom-thinning compounds on crop density and fruit quality of two peach cultivars. Treatments consisted of 15 ml(.)L(-1) and 30 ml(.)L(-1) ammonium thiosulphate, 30 ml(.)L(-1) and 40 ml(.)L(-1) decyl alcohol, and 40 ml(.)L(-1) lime sulfur. Treatments were applied to 'Redhaven' and 'Harrow Diamond' peach trees at two phenological stages: 80%, and 100% full bloom in 2002 and 2003. In both years, treatments reduced the crop density in both cultivars, and in 2003 the amount of hand thinning required to adjust the crop load was significantly reduced. Fruit size from several blossom-thinned treatments was comparable with that observed from hand-thinned trees. However, treatments caused significant leaf phytotoxicity to 'Harrow Diamond' trees in 2003, likely a result of hand spray gun applications. These data indicate that chemical sprays at bloom can be used successfully to reduce fruit set, but are very environmentally, dose, and cultivar dependent.